The present invention relates to silicone polyamic acid which can be photopatterned on various substrates such as glass, silicon, or aluminum and method for making such materials. More particularly, the present invention relates to photopatternable silicone polyamic acid which can be used as an antireflective coating for patterning photoresists, or can be photopatterned on a transparent substrate such as silicon or glass and thereafter imidized to provide for the production of a color filter.
Prior to the present invention, polyamic acid solutions, such as Pyralin polyamic acid, was used to coat various substrates to thicknesses of about 2.5 microns by a standard spinning technique. The applied polyamic acid, a copolymer of pyromellitic dianhydride and 4,4 '--oxydianiline in N-methylpyrrolidone had to be refrigerated during storage at 4.degree. C. maximum, or it readily converted to the insoluble imidized state. As a result, it was difficult to spin dry Pyralin polyamic acid to a tack-free state, prior to applying a positive photoresist to its surface, followed by photopatterning and developing.
Improved polyamic acid photopatterning was achieved by utilizing a silicone polyamic acid, resulting from the intercondensation of benzophenone dianhydride and a polydiorganosiloxane having terminal aminoalkyl groups attached to silicon by silicon-carbon linkages. Although improved adhesion to silicon or glass was achieved with the use of such silicone polyamic acid, as compared to Pyralin polyamic acid, it was found that the problem of premature imidization also occured during the drying of the applied silicone polyamic acid prior to the spin coating of the photoresist. The work-life of the silicone polyamic acid as well as its usefulness during the development of the applied photoresist also was unsatisfactory.
The present invention is based on the discovery that certain silicone polyamic acids, resulting from the use of a siloxane containing norbornane bisanhydride (DiSiAn), shown by Ryang U.S. Pat. No. 4,381,396, assigned to the same assignee as the present invention and incorporated herein by reference, in combination with benzophenone dianhydride (BTADA) and aryldiamine, have been found to resist excessive imidization during the initial drying step of the silicone polyamic acid after its application to a substrate. Temperatures up to 125.degree. C. for a period of 60 minutes can be used to make tack-free silicone polyamic acids which can be readily patterned during the development of a photopatterned photoresist. Surprisingly, the patterned silicone polyamic acid thereafter can be readily removed if used as an antireflective coating. The patterned silicone polyamic acid also can be fully imidized, rendering it substantially insoluble in conventional organic solvents, such as N-methylpyrrolidone in instances where it is used to make a color filter.